Critical Limits of Zinc in Soil and Rice Plant in Valley Soils of Manipur

Abstract

A pot study was conducted to estimate the critical limit of zinc (Zn) in soil and rice plant
in rice growing soils of Manipur. Thirtysix soil samples were collected from different paddy fields of four
valley districts namely Imphal-east, Imphal-west, Thoubal and Bishnupur district of Manipur using
Stratified Random Sampling. All the soil samples were acidic in reaction ranging frompH 4.9 to 6 with
mean value of 5.32, organic carbon content 0.79 to 3.51 %, cation exchange capacity of the soils 8.3 to
24[cmol (p+
) kg-1
] and the clay content of soil varied from 20 to 73.2 % (mean 50.46%). The DTPAextractable Zn showed a positive correlation with dry matter yield (r=0.939**), Bray’s per cent yield
(0.901**), Zn content (0. 977**) and Zn uptake (0.984**). The critical limit of Zn in these soils was
established at 0.78 mg kg-1
for rice and critical limit of 75 days old rice plants is 24.5 mg kg-1
, below
which response to Zn fertilization may be expected. Soil containing Zn below this critical limit may be
responded economically to Zn fertilization for rice growing.